Interesting - friend of mine just picked one up last night as a matter of fact, still in box with manual and cassettes...

Clean the gold contacts with a pencil eraser. Trust me, if it's not a circuit problem, that will fix the problem. Scrub them good but don't go overkill. Blow off the residue with air and maybe wipe them over with alcohol after (I used deoxit). I just went through this last night when we got it back to the shop. A bunch of keys were not firing, and I went through exactly what I said and it's perfect now.